Various methods of facsimile transmission, i.e. the transmission by electrical or optical means of graphic material such as pictures, printed matter, maps, etc., are known. There are four methods of transmission in use; transmission by radio, by land telephone lines, by submarine cable and by the newly developed optical fiber transmission. Each of these introduces its own problems, but the fundamentals of the system are the same for all. The material must be broken into sequential elementary parts which may be transmitted by electrical or optical means and then the parts converted back into a graphic presentation at the receiver. The graphic material is broken into the sequence of elemental parts by the process of scanning. This may be done by mounting the material, e.g. a printed page, on a revolving drum and projecting a small beam of light on or through it. The light is reflected to a phototube with the light and hence the phototube output being proportional to the picture density. The light is moved along the sheet, parallel to the axis of the drum, at such a rate that it displaces axially its own width for each revolution of the drum. Thus, the spot of light progressively scans every spot on the picture. The graphic material can also be scanned by solid-state image sensors such as a charge-coupled device (CCD) or a charge injection device (CID). The output of the phototube is an electrical breakdown of the picture which is modified for transmission and transmitted. At the receiving end, the signal is fed into a recorder which is generally one of two basic types. The first type depends upon the projection of a variable light upon a photographic paper or film resulting in a spot of light whose intensity varies with the varying intensity of the graphic material being transmitted. The other type of recording, to which the present invention may be applied, utilizes a receiving member sensitized to electrical current passage and passes the received signal or another signal triggered by the received signal through it to cause a color change. There are at least four electrolytic mechanisms by which electrical energy can cause the formation of color in a sensitized receiving member, i.e.,
A. BY THE INTRODUCTION OF FOREIGN IONS INTO THE RECEIVING MEMBER;
B. BY THE DISCHARGE OF IONS AT AN ELECTRODE IN CONTACT WITH THE RECEIVING MEMBER;
C. BY INCREASING THE CONCENTRATION OF A PARTICULAR ION AT THE SURFACE OF AN ELECTRODE IN CONTACT WITH THE RECEIVING MEMBER (PH change); and
d. by oxidation or reduction of an electrochromic material at the electrode surface.
The process of the present invention is an improvement to the method designated as (d), that is, the oxidation or reduction of an electrochromic material. An electrochromic material may be defined as a substance whose optical transmission or reflection properties are altered by an interaction with an electronic charge. A persistent electrochromic (PEC) is defined as one which is responsive to the application of an electric field by changing from a first persistent state in which it is essentially non-absorbing to radiation in a given wavelength to a second persistent state which absorbs in that wavelength region. The term persistent indicates that the material can remain in either state when the applied electric field is removed as distinguished from the case of instantaneous reversion to the non-absorbing state when the field is removed.
The use of certain persistent electrochromic materials in imaging systems is disclosed in British Pat. No. 1,186,541 and U.S. Pat. No. 3,521,941. These patents disclose the use of certain transition metal compounds, e.g. molybdenum oxide and niobium oxide, sandwiched between two electrodes so that their color changes when a potential is created between the electrodes. In one example, the first electrode is formed of NESA glass, a commercially available product having a transparent coating of conductive tin oxide on one surface of a glass sheet. The electrochromic material is vacuum deposited onto the tin oxide bearing surface of the glass and a layer of a conductive material, e.g. gold, is deposited onto the surface to form a sandwich of the electrochromic material between the electrodes. The patents disclose a preferred embodiment in which an insulating layer is deposited between one of the electrodes and the electrochromic material which is said to render the electrochromic layer more sensitive to a field of opposite polarity to return it to the absorption characteristic state it occupied prior to the application of the field. A plate containing such an insulating material is disclosed as being imaged by a movable probe or stylus for use in information storage and transmission and the so-formed image is taught to be erasable by rubbing a relatively broad area electrode across the surface of the plate with the potentials suitably reversed.
The above-described three-layered system, i.e., NESA glass, electrochromic material and conductive overcoating, suffers from two disadvantages. The first is that it does not have the requisite flexibility for use in conventional drum-type facsimile receivers in which a sheet of recording paper is wrapped around a rotating drum with a stylus mounted to move perpendicular to the direction of drum rotation used as the movable electrode. The second is that it is not self-fixing since once the plate is fabricated and imaged, it can be reimaged to the point of obliterating the intelligence contained thereon from the initial imaging by the application of a potential between the electrodes. The four-layered structure suffers from a further disadvantage since the application of the insulating layer requires an extra fabricating step in addition to rendering the plate even more inflexible.
It would be desirable, and it is an object of the present invention to provide a novel system for the creation of images by the conversion of a persistent electrochromic material from a first absorptive state to a second absorptive state in which it absorbs light of the desired wavelength.
A further object is to provide a novel process for recording graphic material in a facsimile transmission system.
An additional object is to provide such a process in which the graphic material is recorded by converting a persistent electrochromic material from a non-absorbing state to an absorbing state in imagewise configuration corresponding to the image being transmitted.
A further object is to provide such a process in which the persistent electrochromic material is distributed on a flexible substrate which can be wrapped around a drum in a facsimile receiving apparatus.
An additional object is to provide such a process in which the image is fixable so as to render it immune from further imaging.